1. Field of the Invention
The present invention refers to a needle protection means for injection devices comprising a first sleeve, a second sleeve that can be slid into or over the first sleeve and a force element functioning between the two sleeves, wherein a pressure or trigger point must be overcome to displace the second sleeve
Today, the term injection device is used for simple syringes as well as complex, dosable injection devices that, as their design resembles that of writing tools, are referred to as pens.
2. Description of Related Art
Such pens are known from WO 93/16740. They contain a sleeve-like main body which can be divided into two main areas: a distal area (facing away from the patient) containing a discharge mechanism and a proximal area (facing towards the patient) that contains the fluid to be administered. At the proximal end of the main body a needle and needle holder are attached that allow the discharge of the liquid from the device; such known needles are, for instance, PENFINE.RTM. needles as described in WO 95/01812.
In many cases, the liquids to be administered are not directly located in the main body but in an ampoule, with the liquid being stored between a piercable membrane and a displaceable piston.
By activating the discharge mechanism, the piston of the ampoule is pushed into the proximal direction so that fluid is discharged through the needle.
For psychological reasons, many patients find it difficult to inject themselves, as a fully visible needle has to penetrate the skin. Needle protection means that only enclose the needle and thus hide the needle from the patient's view during penetration are known from WO 93/05835. A sleeve-like part whose proximal edge is placed onto the skin of the user during an injection process, glides in distal direction when the injection device is displaced in proximal direction.
U.S. Pat. No. 5,609,577 describes a device that prevents a premature or unintentional penetration of the skin by the needle of an injection means.
In many cases, however, not only the visibility of the needle is a problem for patients but also the awareness that a movement of the injection device in proximal direction by the patient pushes the needle under the skin. For this reason, so-called auto-injectors were developed that automatically puncture the skin with the needle and discharge the drug after activation. Such devices are, for instance, known from EP-A-0 268 191.